Complementary heterogeneous MOSFET using global SiGe substrate and hard-mask memorized germanium dilution for nFET

ABSTRACT

A method includes providing a substrate that underlies a layer of SiGe; forming a plurality of fins in the layer of SiGe. Each formed fin has a fin shape and fin location preserving hard mask layer on a top surface. The method also includes depositing Si on a first subset of the set of fins in what will be an nFET area; performing a Si—Ge inter-mixing process on the first subset of fins to reduce a concentration of Ge in the first subset while producing a Si—Ge intermix layer; removing the Si—Ge intermix layer leaving the first subset of fins having the reduced concentration of Ge, and forming a second subset of fins in what will be a pFET area. The second subset is also formed from the layer of SiGe and has a greater percentage of Ge than a percentage of Ge in the first subset of fins.

CROSS-REFERENCE TO A RELATED US PATENT APPLICATION

This patent application is a continuation application of copending U.S.patent application Ser. No. 14/817,549, filed on Aug. 4, 2015, and isfurther related to copending U.S. patent application Ser. No.15/133,525, filed on Apr. 20, 2016, the disclosures of which areincorporated by reference herein in their entireties.

TECHNICAL FIELD

The various embodiments of this invention relate generally tosemiconductor devices and fabrication techniques and, more specifically,relate to the fabrication of semiconductor transistor devices composedof Si and SiGe on a common substrate.

BACKGROUND

Tensile strained silicon (s-Si) enhances electron mobility by liftingthe conduction band degeneracies, reducing carrier scattering andincreasing the population of carriers in sub-bands with lower transverseeffective mass. Channel engineering using Si or s-Si for an nFET andcompressive strained SiGe for a pFET is a viable option for realizingsmall geometry devices while meeting performance targets. Multipleepitaxial deposition approaches might potentially be used forfabricating nFETs and pFETs, however the design rules and epitaxialnon-idealities such as corner rounding, thickness and surface controllimit the heterogeneous integration of Si and SiGe.

SUMMARY

In a first aspect thereof the embodiments of this invention provide amethod that comprises providing a substrate that underlies a layer ofSiGe; forming a plurality of fins in the layer of SiGe, each formed fincomprising a hard mask layer on a top surface; depositing Si on a firstsubset of the set of fins in what will be an nFET area; performing aSi—Ge inter-mixing process on the first subset of fins to reduce aconcentration of Ge in the first subset of fins while producing a Si—Geintermix layer; removing the Si—Ge intermix layer leaving the firstsubset of fins having the reduced concentration of Ge and forming asecond subset of fins in what will be a pFET area, the second subset offins being formed from the layer of SiGe and having a greater percentageof Ge than a percentage of Ge in the first subset of fins.

In another aspect thereof the embodiments of this invention provide astructure that comprises a substrate and a first subset of fins definedin an nFET area of the structure. The first subset of fins is comprisedof tensile strained substantially pure Si formed from an initialsemiconductor layer disposed over the substrate, where the initialsemiconductor layer is comprised of a layer of Si_(1-x)Ge_(x) having afirst value of x. The structure further comprises a second subset offins defined in a pFET area of the structure. The second subset of finsis comprised of compressive strained Si_(1-x)Ge_(x) formed from theinitial semiconductor layer and has a second value of x that is greaterthan the first value of x. In the structure each fin of at least thefirst subset of fins is comprised of an overlying hard mask layer thatpreserves a location and shape of the first subset of fins during aprocess to reduce the value of x in the initial semiconductor layer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1-17 are each an enlarged cross-sectional view showing variousinitial, intermediate and completed or substantially completedstructures that are fabricated in accordance with a first and a secondembodiment of this invention, wherein the various layer thicknesses andother dimensions are not necessarily drawn to scale. More specifically:

FIGS. 1-6 pertain to the first embodiment of this invention, whereinFIG. 1 illustrates a starting structure comprised of a bulk Sisubstrate, an overlying oxide layer (buried oxide layer or BOX), astrained SiGe layer formed on the BOX and a plurality of hard masks(HMs) disposed on the SiGe layer;

FIG. 2 shows the structure of FIG. 1 after formation of a plurality offins in the SiGe layer, each fin underlying one of the HMs;

FIG. 3 shows the structure of FIG. 2 after formation of a mask over afirst sub-set of the fins (fins that will be pFET fins) and the growthof a layer of Si on exposed sidewall surfaces of the s-SiGe fins;

FIG. 4 shows the structure of FIG. 3 after performing a Ge—Si intermixprocess to dilute the Ge in the s-SiGe fins and form diluted SiGe;

FIG. 5 shows the structure of FIG. 4 after removing the diluted SiGe;

FIG. 6 shows the structure of FIG. 5 after removing the masks leavingthe s-SiGe fins in a pFET area and Ge-depleted (e.g., almost pure Si)diluted fins in an nFET area.

FIGS. 7-17 pertain to the second embodiment of this invention, whereinFIG. 7 illustrates a starting structure comprised of a bulk Sisubstrate, an overlying oxide layer (buried oxide layer or BOX), astrain-relaxed SiGe layer formed on the BOX and a plurality of hardmasks (HMs) disposed on the SiGe layer;

FIG. 8 shows the structure of FIG. 7 after formation of a mask 40 (e.g.,an oxide) where a first sub-set of fins will be formed, i.e., those finsthat will be pFET fins in the final structure;

FIG. 9 shows the structure of FIG. 8 after selectively removing thestrain-relaxed SiGe to define a second sub-set of fins formingstrain-relaxed SiGe fins 38 that will be nFET fins in the finalstructure;

FIGS. 10, 11 and 12 correspond to the process of FIGS. 3, 4 and 5,respectively, wherein FIG. 10 illustrates the growth a layer of Si onexposed sidewall surfaces of the strain-relaxed SiGe fins;

FIG. 11 shows the structure of FIG. 10 after performing thehigh-temperature Ge—Si intermix process and forming diluted SiGe;

FIG. 12 shows the structure of FIG. 11 after removing the diluted SiGeleaving diluted SiGe fins;

FIG. 13 shows the structure of FIG. 12 after removing the pFET mask andforming an nFET mask;

FIG. 14 shows the structure of FIG. 13 after forming a nitride spaceraround each of the HMs in the pFET area to widen the HMs;

FIG. 15 shows the structure of FIG. 14 after removing those portions ofthe strain-relaxed SiGe layer not covered by the widened HMs leavingstrain-relaxed Si_(1-x)Ge_(x) fin precursor structures;

FIG. 16 shows the structure of FIG. 15 after performing a condensationprocess for the strain-relaxed Si_(1-x)Ge_(x) fin precursors to increasethe Ge percentage, reduce the width and form a layer of thermal oxide;and

FIG. 17 shows the structure of FIG. 16 after removing the nFET mask, theHMs and nitride spacers and the thermal oxide, thereby leaving thehigher Ge percentage SiGe fins in a pFET area and the Ge-depleted (e.g.,almost pure Si) diluted fins in an nFET area.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments. All of the embodiments described inthis Detailed Description are exemplary embodiments provided to enablepersons skilled in the art to make or use the invention and not to limitthe scope of the invention which is defined by the claims.

The terms “epitaxial growth and/or deposition” and “epitaxially formedand/or grown” mean the growth of a semiconductor material on adeposition surface of a semiconductor material, in which thesemiconductor material being grown has the same crystallinecharacteristics as the semiconductor material of the deposition surface.In an epitaxial deposition process, the chemical reactants provided bysource gases are controlled and the system parameters are set so thatthe depositing atoms arrive at the deposition surface of thesemiconductor substrate with sufficient energy to move around on thesurface and orient themselves to the crystal arrangement of the atoms ofthe deposition surface. Therefore, an epitaxial semiconductor materialhas the same crystalline characteristics as the deposition surface onwhich it is formed. For example, an epitaxial semiconductor materialdeposited on a {100} crystal surface will take on a {100} orientation.In some embodiments, epitaxial growth and/or deposition processes areselective to forming on semiconductor surface, and do not depositmaterial on dielectric surfaces, such as silicon dioxide or siliconnitride surfaces.

Examples of various epitaxial growth process apparatuses and methodsthat are suitable for use in implementing the embodiments of thisinvention can include, but are not limited to, chemical vapor deposition(CVD) such as, for example, rapid thermal chemical vapor deposition(RTCVD), atmospheric pressure chemical vapor deposition (APCVD), lowpressure chemical vapor deposition (LPCVD) and ultra-high vacuumchemical vapor deposition (UHVCVD). Other suitable epitaxial growthprocesses can include, but are not limited to, molecular beam epitaxy(MBE) and low-energy plasma deposition (LEPD). The temperature for anepitaxial deposition process typically ranges from about 550° C. toabout 900° C. Although higher temperature will typically result infaster deposition of the semiconductor material, the faster depositionmay also result in crystal defects and film cracking.

In at least one embodiment thereof this invention can employsemiconductor on insulator (SOT) technology where a thin semiconductorlayer, such as a layer of SiGe or a layer of Si, is formed over aninsulating dielectric layer, such as a layer of silicon oxide, which inturn is formed over a (bulk) substrate, such as a Si substrate. Theinsulating layer can be referred to as a buried oxide (BOX) layer orsimply as a BOX. For a single BOX SOI wafer the SOI layer can be dividedinto active regions by shallow trench isolation (STI) which intersectsthe BOX and provides total isolation for active device regions formed inthe SOI layer. For FinFET devices fin structures can be defined in theSOI layer and sources and drains can be formed, for example, by ionimplantation of N-type or P-type dopants into the fins. A FET channelregion between a source/drain pair can be created so as to underlie agate structure.

The embodiments of this invention pertain at least in part to theheterogeneous integration of SiGe (compressive) and Si (relaxed ortensile) on a common wafer, such as a SOI wafer. The use of theembodiments of this invention provides a number of advantages andbenefits. These include, but are not limited to, the following examples.The process begins with globally relaxed or strained SiGe film oninsulator (SOI) and thus no epitaxial adjustment is needed before finpatterning. The initial thickness of the film controls the final finheight for both nFETs and pFETs. In addition, the nFET Ge content isdiluted by epitaxy of Si on fin sidewalls and by an intermix processthat is performed to dilute the Ge, followed by RIE to remove theintermixed SiGe. A nitride hard mask (HM) that is used on top of thefins has a memory effect for both fin location and fin width, therebypreserving the dimensions of the nFETs during processing. In addition,the process of Si epitaxy, Ge dilution and RIE can be repeated multipletimes in order to achieve almost pure Si fins for the nFETs, while theHM memory effect results in a fixed fin width. In a further embodiment,where relaxed SiGe can be used as starting material, there is provided acombination of the HM memorized dilution and a Ge condensation processto achieve tensile s-Si for nFETs and compressive s-SiGe for pFETs.

FIGS. 1-6 pertain to a first embodiment of this invention. FIG. 1 showsa starting structure (starting wafer) that can be comprised of a Sisubstrate 10 of arbitrary thickness, an overlying BOX 12 and a layer 14of s-Si_(1-x)Ge_(x) (e.g., where x˜0.20). The layer 14 ofs-Si_(1-x)Ge_(x) could have a thickness of about 35 nm±15 nm. The layer14 of s-SiGe can be formed using, for example, Ge intermix or Ge thermalcondensation processes. It is preferred that the layer 14 ofs-Si_(1-x)Ge_(x) be approximately or substantially lattice-matched tothe Si substrate 10. Also shown in FIG. 1 is the result of patterning anitride hard mask (HM) layer to form a plurality of HMs 16. Each islocated at a position where a fin is desired to be formed in the layer14 of s-Si_(1-x)Ge_(x).

FIG. 2 shows the structure of FIG. 1 after formation of a plurality offins 18 in the SiGe layer 14, where each fin 18 underlies one of the HMs16. The fins 18 can be formed by a reactive ion etch (RIE) process usingany suitable chemistry that is selective to the material of the BOX 12.Examples include chlorine-based and bromine-based etch chemistries. Eachfin 18 has a height, relative to the top surface of the BOX 12, that isthe same as the thickness of the layer 14 of s-Si_(1-x)Ge_(x), e.g.,about 35 nm±15 nm and can have a width governed by the width of theoverlying HM 16, e.g., about 7 nm to about 14 nm (or greater). The finlength can have any desired value depending on the end use.

FIG. 3 shows the structure of FIG. 2 after formation of a mask 20 (e.g.,an oxide) over a first sub-set of the fins 18, i.e., those s-SiGe fins18 that will be pFET fins in the final structure, thereby leavingexposed a second sub-set of the fins 18 that will be nFET fins in thefinal structure. Next the method selectively grows a layer 22 of Si onexposed sidewall surfaces of the s-SiGe fins 18. A CVD process (e.g.,rapid thermal CVD) can be used for this purpose. The Si layer 22 can beformed by the epitaxial growth of Si on the exposed surfaces of the SiGefins 18 using a mixture of silane and dichlorosilane. The HMs 16 providea “memory” effect that records the locations (and widths) of theoriginal fins 18.

FIG. 4 shows the structure of FIG. 3 after performing a high-temperature(e.g., 1000° C.) Ge—Si intermix process where Ge in the fins 18 diffusesinto the Si layer 22 and where Si in the layer 22 diffuses into the SiGefins 18. Due to the dominance of the Si in the grown Si layers 22 duringthis inter-diffusion process the Ge of the SiGe fins 18 is diluted. Asan example, and considering an exemplary 7 nm SiGe fin width, a 32 nmfin pitch (the space between fins 18 now occupied by the grown Si 22)and an initial Ge percentage of 20% in the SiGe fins 18, the Gepercentage can be diluted to about 4.3% during the Ge—Si intermixprocess. This process produces what may be referred to as a Si—Geintermix layer that is comprised of diluted SiGe 24. FIG. 5 shows thestructure of FIG. 4 after removing the diluted SiGe 24 by any suitableRIE or other type of etch procedure, thereby leaving diluted SiGe fins26 each still covered by their respective HMs 16. There are certain RIEprocesses that can etch SiGe selective to the nitride HM 16. As but onenon-limiting example, HBr/He/O₂/He can be used for this purpose.

In accordance with a non-limiting aspect of this invention the steps ofFIGS. 3, 4 and 5 can be iterated any desired number of times to grow theSi 22 (FIG. 3), perform the Ge—Si intermix process (FIG. 4) and thenremove the resulting diluted SiGe 24 (FIG. 5). After each such iterationthe Ge content of the diluted SiGe fins 26 is reduced further. In otherwords, the steps of FIGS. 3, 4 and 5 can be repeated as needed toasymptotically approach a desired, e.g., a substantially zero, Gepercentage in the fins 26. This iterative process can result inproducing substantially pure (tensile strained) Si fins for the nFETs tobe fabricated.

By “substantially pure” Si fins what is meant is that the percentage ofGe is reduced to, for example, less than about 5%, or more preferablyless than about 3%, or even more preferably less than about 1% so as toresult in a tensile-strained Si-containing fin that can function as annFET in a final circuit.

FIG. 6 shows the structure of FIG. 5 after removing the pFET mask 20 andthe HMs 16 leaving the s-SiGe fins 18 in a pFET area 28A and theGe-depleted (e.g., substantially pure Si) diluted fins 26 in an nFETarea 28B. In this embodiment the s-SiGe fins 18 and the diluted SiGefins 28 can have substantially equal fin widths that are established(and maintained during nFET processing) by the width of the HM 16.Processing can then continue in a conventional manner to formsource/drains (S/Ds), gate structures, dielectric layer deposition(s)and vertical and horizontal metallization as needed for the finalcircuitry.

FIGS. 7-17 pertain to a second embodiment of this invention. FIG. 7shows a starting structure (starting wafer) that can be comprised of aSi substrate 30 of arbitrary thickness, an overlying BOX 32 and a layer34 of strain-relaxed Si_(1-x)Ge_(x) (e.g., where x˜0.25). The top layer34 of strain-relaxed Si_(1-x)Ge_(x) could have a thickness of about 35nm+15 nm. The layer 34 can be provided, for example, by a wafer bondingprocess, where after wafer bonding a handle wafer is removed and thelayer 34 is thinned to the desired thickness. A high temperature anneal(e.g., 1200° C. to 1300° C.) could also be used to relax a s-SiGe layerthat is formed using, for example, Ge intermix or Ge thermalcondensation processes. As in the embodiment of FIGS. 1-6 it ispreferred that the layer 34 of strain-relaxed Si_(1-x)Ge_(x) beapproximately lattice-matched to the Si substrate 30. Also shown in FIG.7 is the result of patterning a nitride hard mask (HM) layer to form aplurality of HMs 36. Each HM 36 is located at a position on the surfaceof the strain-relaxed Si_(1-x)Ge_(x) layer 34 where a fin is desired tobe formed.

FIG. 8 shows the structure of FIG. 7 after formation of a mask 40 (e.g.,an oxide) where a first sub-set of fins will be formed, i.e., those finsthat will be pFET fins in the final structure.

FIG. 9 shows the structure of FIG. 8 after performing an RIE procedureto selectively remove the strain-relaxed SiGe 34 to define a secondsub-set of fins forming strain-relaxed SiGe fins 38 that will be nFETfins in the final structure. Each of the fins 38 has a width and alength defined by the overlying HM 36 and is disposed on the surface ofthe BOX 32. A height of each of the strain-relaxed SiGe fins 38corresponds to the thickness of the strain-relaxed SiGe layer 34 or, inthis non-limiting embodiment, about 35 nm±15 nm.

FIGS. 10, 11 and 12 correspond to the process described above for FIGS.3, 4 and 5, respectively. More specifically, FIG. 10 illustrates thegrowth a layer 42 of Si on exposed sidewall surfaces of thestrain-relaxed SiGe fins 38. As in FIG. 3, a CVD process (e.g., rapidthermal CVD) can be used for this purpose. The Si layer 42 can be formedby the epitaxial growth of Si on the exposed surfaces of thestrain-relaxed SiGe fins 38 using a mixture of silane anddichlorosilane, and the HMs 36 provide a “memory” effect that recordsthe locations (and widths) of the original fins 38. FIG. 11 shows thestructure of FIG. 10 after performing the high-temperature (e.g., 1000°C.) Ge—Si intermix process where Ge in the fins 38 diffuses into the Silayer 42 and where Si in the layer 42 diffuses into the SiGe fins 38.Due to the dominance of the Si in the grown Si layers 42, during thisinter-diffusion process the Ge of the strain-relaxed SiGe fins 38 isdiluted. As an example, and considering again an exemplary 7 nm width ofthe strain-relaxed SiGe fins 38, a 32 nm fin pitch and an initial Gepercentage of 25% in the strain-relaxed SiGe fins 38, the Ge percentagecan be diluted to a range of about 5%-6% during the Ge—Si intermixprocess. FIG. 12 shows the structure of FIG. 11 after removing thediluted SiGe 44 by any suitable RIE or other type of etch procedure,thereby leaving diluted SiGe fins 46 each still covered by theirrespective HMs 16.

As with the embodiment of FIGS. 3, 4 and 5, and further in accordancewith a non-limiting aspect of this invention, the steps of FIGS. 10, 11and 12 can be iterated any desired number of times to grow the Si 42(FIG. 10), perform the Ge—Si intermix process (FIG. 5) and then removethe resulting diluted SiGe 44 (FIG. 12). After each such iteration theGe content of the diluted SiGe fins 26 is reduced further. Thus, thesteps of FIGS. 10, 11 and 12 can be repeated as needed to asymptoticallyapproach a desired, e.g., a substantially zero, Ge percentage in thediluted strain-relaxed fins 46. The use of this iterative process canresult in producing substantially pure (tensile strained) Si fins forthe nFETs to be fabricated.

FIG. 13 shows the structure of FIG. 12 after removing the pFET mask 40and forming an nFET mask 48 to cover the diluted strain-relaxed fins 46and their corresponding HMs 36.

FIG. 14 shows the structure of FIG. 13 after forming a nitride spacer 50around each of the HMs 36 in the pFET area. The nitride spacers 50 serveto widen the HMs 36. The width of the nitride spacer can be in a rangeof about 4 nm to about 12 nm, whereas the width of the original HM 36can be in a range of about 5 nm to about 20 nm.

FIG. 15 shows the structure of FIG. 14 after performing an RIE procedureto remove those portions of the layer 34 of strain-relaxedSi_(1-x)Ge_(x) not covered by the widened HMs (the HM 36 and surroundingnitride spacer 50). The end result of the RIE process is the formationof what may be referred to as strain-relaxed Si_(1-x)Ge_(x) finprecursors 36A.

FIG. 16 shows the structure of FIG. 15 after performing a condensationprocess for the strain-relaxed Si_(1-x)Ge_(x) fin precursors 36A. Thecondensation process involves performing an anneal operation. Onesuitable but not limiting range of temperature is about 700° C. to about1000° C. for a period of some minutes. In a case where the annealprocess involves oxidation, the oxygen reacts with silicon in theSi_(1-x)Ge_(x) fin precursors 36A to form thermal silicon oxide 54.Meanwhile, Ge is repelled towards the core of the Si_(1-x)Ge_(x) finprecursors 36A. As a result, the Ge concentration in a final SiGe fin isincreased after oxidation. Such a Ge enrichment process can be referredto without limitation as “condensation”. In the condensed (Ge enriched)Si_(1-x)Ge_(x) fins, referred to in FIG. 16 as the higher Ge % SiGe 52,the value of x can be, for example, about 0.50, and the width (notconsidering the overlying oxide 54, is reduced by the oxidation processfrom a starting value of, for example, about 12 nm-14 nm to a finalvalue of, for example, about 6 nm-7 nm.

In this exemplary method of the second embodiment the strain-relaxedlayer 34 of SiGe can be a layer of Si_(1-x)Ge_(x) where x has a non-zerovalue=n. In this method forming the first subset of fins related to pFETcircuitry can comprise annealing the first subset of fins to form a setof condensed Si_(1-x)Ge_(x) fins, where x has a value=m, where m>n. Thestep of annealing forms an oxide layer 54 that covers at least verticalsurfaces of individual ones of the set of condensed Si_(1-x)Ge_(x) fins.In this method n can be equal to about 0.25, and m can be equal to about0.50. Individual ones of the first subset of fins related to pFETcircuitry have a first width. In this embodiment the annealing consumessome of the Si_(1-x)Ge_(x) of the fins to form the oxide, and individualones of the fins of the first subset of fins have a second width that isless than the first width.

FIG. 17 shows the structure of FIG. 16 after removing the nFET mask 48,the HMs 36, the nitride spacers 50 and the thermal oxide 54, therebyleaving higher Ge percentage (e.g. x=0.50) SiGe fins 46 in a pFET area58A and the Ge-depleted (e.g., almost pure Si) diluted fins 46 in annFET area 58B. In this embodiment the s-SiGe fins 18 and the dilutedSiGe fins 28 can have substantially equal fin widths that areestablished (and maintained during nFET processing) by the width of theHM 16 in conjunction with the spacers 50 and the condensation process.Processing can then continue in a conventional manner to formsource/drains (S/Ds), gate structures, dielectric layer deposition(s)and vertical and horizontal metallization as needed for the finalcircuitry.

It is noted that any one of the structures shown in FIGS. 1-17 could beviewed as an intermediate structure formed during the overall process offorming a final structure. It is also noted that references to first andto second subsets of fins in this description and in the claims canrefer to either of the pFET fins or the nFET fins, depending on thecontext of the reference.

It is to be understood that although the exemplary embodiments discussedabove with reference to FIGS. 1-17 can be used on common variants of theFET device including, e.g., FET devices with multi-fingered FIN and/orgate structures and FET devices of varying gate width and length.Moreover, transistor devices can be connected to metalized pads or otherdevices by conventional ultra-large-scale integration (ULSI)metalization and lithographic techniques.

Integrated circuit dies can be fabricated with various devices such as afield-effect transistors, bipolar transistors, metal-oxide-semiconductortransistors, diodes, resistors, capacitors, inductors, etc. Anintegrated circuit in accordance with the present invention can beemployed in applications, hardware, and/or electronic systems. Suitablehardware and systems in which such integrated circuits can beincorporated include, but are not limited to, personal computers,communication networks, electronic commerce systems, portablecommunications devices (e.g., cell phones), solid-state media storagedevices, functional circuitry, etc. Systems and hardware incorporatingsuch integrated circuits are considered part of this invention. Giventhe teachings of the invention provided herein, one of ordinary skill inthe art will be able to contemplate other implementations andapplications of the techniques of the invention.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

As such, various modifications and adaptations may become apparent tothose skilled in the relevant arts in view of the foregoing description,when read in conjunction with the accompanying drawings and the appendedclaims. For example, the use of other similar or equivalentsemiconductor fabrication processes, including deposition processes andetching processes may be used by those skilled in the art. Further, theexemplary embodiments are not intended to be limited to only thosetemperature ranges, semiconductor materials, Ge concentrations,dielectrics, layer thicknesses and the like that were specificallydisclosed above. Any and all such and similar modifications of theteachings of this invention will still fall within the scope of thisinvention.

What is claimed is:
 1. A structure comprising: a substrate; a firstsubset of fins defined in an nFET area of the structure, the firstsubset of fins being comprised of tensile strained substantially pure Siformed from an initial semiconductor layer disposed over the substrate,the initial semiconductor layer being comprised of a layer ofSi_(1-x)Ge_(x) having a first value of x; and a second subset of finsdefined in a pFET area of the structure, the second subset of fins beingcomprised of compressive strained Si_(1-x)Ge_(x) formed from the initialsemiconductor layer and having a second value of x that is greater thanthe first value of x; where each fin of at least the first subset offins is comprised of an overlying hard mask layer that preserves alocation and shape of the first subset of fins during a process toreduce the value of x in the initial semiconductor layer.
 2. Thestructure as in claim 1, where the process comprises iterated steps ofdepositing Si on the first subset of the set of fins, performing a Si—Geintermixing process and removing a resultant Si—Ge intermix layer. 3.The structure as in claim 1, further comprising a dielectric layerdisposed between each of the first and second subsets of fins and thesubstrate.
 4. The structure as in claim 3, where the substrate iscomprised of Si.
 5. The structure as in claim 3, where the initial layerof semiconductor material is substantially lattice matched to the Sisubstrate.
 6. A structure comprising: a substrate; a first subset offins defined in an nFET area of the structure, the first subset of finsbeing comprised of tensile strained substantially pure Si formed from aninitial semiconductor layer of Si—Ge disposed over the substrate; and asecond subset of fins defined in a pFET area of the structure, thesecond subset of fins being comprised of compressive strained Si—Geformed from the initial semiconductor layer and having a greaterpercentage of Ge than a percentage of Ge in the first subset of fins;where each fin of at least the first subset of fins is comprised of anoverlying hard mask layer that preserves a location and shape of thefirst subset of fins during a process to reduce the amount of Ge in theinitial semiconductor layer of Si—Ge.
 7. The structure as in claim 6,where the process comprises iterated steps of depositing Si on the firstsubset of the set of fins, performing a Si—Ge intermixing process andremoving a resultant Si—Ge intermix layer.
 8. The structure as in claim6, further comprising a dielectric layer disposed between each of thefirst and second subsets of fins and the substrate.
 9. The structure asin claim 8, where the substrate is comprised of Si.
 10. The structure asin claim 8, where the initial layer of semiconductor material issubstantially lattice matched to the Si substrate.